Recent years have seen an increase in the number of movie theaters capable of presenting stereoscopic display and thus offering opportunities to enjoy 3D video. Also, 3D television receivers and 3D players offering opportunities to watch 3D video as well as 2D video at homes are becoming widespread.
When the display screen of a display device is perceived as an X-Y plane, a 2D video image is an image presented by image pixels on this X-Y plane, and may also be referred to as a monoscopic image.
On the other hand, a 3D video is composed of images that add depth in the direction of the Z axis to the image pixels on the X-Y plane of the display screen of the display device. 3D video is viewed by the user through playback of the left-view images to be perceived by the left eye and the right-view images to be perceived by the right eye to produce the stereoscopic viewing effect.
With reference to pixels of a 3D video image, pixels having a positive Z-axis coordinate appear in the user's eye closer toward the user than the actual display screen of the display device, whereas pixels having a negative Z-axis coordinate appear further back than the display screen.
Here, the depth of captions (or subtitles) presented with 3D video images, such as a 3D movie production, needs to be adjusted in view of the degree of pop out of the 3D video images. Without the depth adjustment, captions may appear to stick out from the video images, or the captions may appear too far apart in depth direction from the video images.
In view of such problems, it is desirable to optimally adjust the depth or of the pop-out state of each caption or frame to make the captions appear slightly closer than the video images.
Patent Literature 1 and 2 listed below describe a conventional technology for optimally adjusting captions displayed on 3D video images to realize playback of superior quality stereoscopic images.